Aluminum bronze alloy containing chromium and having improved wear resistance



' nite This invention relates to an'aluminum bronze alloy and moreparticularly to an aluminum bronze alloy having improved corrosionresistance, toughness and wearres'istance.

rates atent Aluminum bronze alloys have for years been used :as

dies for forming and --drawing operations for a large group of sheet andplate alloys, such as stainless steel, aluminum, nickel, titanium, mildsteel and some copper zbase alloys. Aluminum bronze alloys used '-'indie applications possess-the properties of good corrosion resistance,wear resistance and non-galling against many wrought materials. I

The aluminum bronze alloys which in the past have shown-the optimumproperties for deep drawing dies are those that contain approximately14% aluminum, a small amount of'iron and the balance copper. An alloy ofthis *type has'good corrosion resistance and non-gelling properties.'However, under heavy use in die application, this alloy sometimeswea'rsundesirably fast so that close dimensional tolerances cannot bemaintained because of the wear that occurson the die surface.

"The present invention is directed to an aluminum bro'nze alloy havingthe non-galling properties characteristic of "aluminum bronze alloys buthaving greatly improved corrosion -resistance, 'wear resistance andtoughness. This is accomplished by the addition of a small amount ofchromium to the alloy which renders the alloy less susceptible :toeutectoid transformation and its em- ,hrittling structure.

' The alloy .of the invention'has the following general composit on byWeight 1 Percent Aluminum 13.0-20.0

Iron r, 1.0-8.0 Chromium 0.5-3.0 Copper Balance v A specificillustration of the composition falling within the above range is asfollows in weight percent:

Percent Aluminum 13.01 Iron 4.13 Chromium 1.51 Copper 81.35

The wear resistance of the alloy of the invention is substantiallyimproved over that of aluminum bronze alloys which do not contain thechromium. The data contained .in the following table shows the improvedwear resistance of the alloy of the invention over similar aluminumbronze alloys which do not contain the chromium addition:

Patented July 12,1960

The draws set forth in the above table were made on production pressesdrawing stainless steel parts for barrels and the results clearly showthe superiority of the present alloy in regard'to wear resistance overthat of the other alloys which do .not contain the chromium addition.As-shown in the table, 134,-493 :draws were made with the die fabricatedfrom the :present alloy before it was necessary to redress the die dueto loss of dimensional tolerance caused :by wear, 'while the alloysamples 1 and 2, which did not contain the chromium addition, had to beredressed after only 77,000 and 93,190 draws, respectively.

The increase in thewear resistance of the alloy with the addition ofchromium ;is particularly surprising since the hardness o'f-the alloycontaining chromium is less than the hardness of the alloys which do notcontain chromium, as shown in the table. With'the decrease in hardness,it would be expected that the wear resistance of the alloy would becorrespondingly decreasedg'how ever, the opposite is true with respectto the alloy of the invention.

The alloy of the invention containing about 13% aluminum, 4% iron, 1.5%chromium and the balance copper can be cast statically or centrifugallyto produce a fine grain tough structurehaving a hardness ofapproximately 32 Rockwell C. The hardness of the alloy can be variedwithin the range of 25 Rockwell 'C'to 55 Rockwell C depending upon thespecific aluminum and chromium contentin the alloy.

The alloy with the above composition has unusual compressive strengthand test specimens have been as high as 200,000 p.s.'i. inult'imatecompression. A centrifugally cast alloy of the above composition'ha-s atensi'lestrength of about 100,000 p.s.i., while a statically 'castalloy'has a tensile strength of'about 80,000 p.s.'i.

The 'metallographic structure of the alloy consists essentially of gammatwo phase which is uniformly distributed in a matrix of beta. Anintermetallic compound composed of iron, aluminum, copper and chromiumexists in rosette and spheroid particles and is uniformly disresistanceand also makes the alloy less susceptible :to

the eutectoid transformation. The eutectoid structure consists of alphaphase plus gamma two phase formed from the transformation-dccompositionof the beta phase. This transformation occurs at temperatures below 1050F. in aluminum bronze alloys and the resultant eutectoid structure isbrittle and possesses low ductility and poor machinability.

The chromium also provides a finer grain structure which enables thealloy to be machined to a better finish.

In order to obtain optimum properties, the metals used with the alloyshould be of high quality. Electrolytic or wrought fire refined copper,high purity aluminum, low carbon iron and high purity chromium arepreferred to be used. It hasbeen found that a very satisfactory methodof obtaining the desired uniformity in the alloy is by using a doublemelting procedure whereby a pre-alloy is made. The most satisfactorypre-alloy is one that has approximately 50% aluminum, 20% copper, 20%iron and 10% chromium. The chromium can be added to the pre-alloy in theform of powdered briquets containing 35 chromium and the balance copper.

The melting procedure employed in making the prealloy is such that somecopper, along with the iron and chromium, is placed into the crucibleand melting begun. When the copper starts to melt, the iron and otheradditives are slowly dissolved into the copper during the period whenaluminum is added to form an exothermic re- 7 action which helps todissolve the higher melting point chromium addition. This form and isready to use for the final alloy.

Alternately, instead of adding the chromium to the pre-alloy, thechromium can be added to the final alloy. In" this case, an alloy ofchromium and 90% copper is added to the final alloy. v

To establish complete uniformity of the micro-strucpre-alloy is thencast into ingot ture and hardness, the alloy is heattreated at ,anelevated temperature in the range of 1050 F. to 1400 R, such as about1150 F. Small castings of simple shapes of this alloy can be placeddirectly into the heat. treating furnace at temperature. Large massivecastings-or intlicate pes are preheated in the furnace at about 400 1.

20 F. per hour per one inch of section thickness. This 7 rate isconveniently obtained by fan air cooling.

Internal stresses created within castings during machining or otherfinishing operations, during weldrnents, or from metal overlays on basemetals, are usually re.- moved depending on the future application ofthe part. These stresses are removed by a stress relief heat treatment.

To stress relieve the alloy, the alloy is heated;to a temperaturebelow600 F. and maintained at this temperature for a period up to 3 hours perone inch of section thickness. The article is then cooled to roomtemperature. More specifically, to stress relieve the alloy, the alloyis heated to a temperature of 500 F. and maintained at this temperaturefor approximately 2 hours per one inch of section thickness.

The alloy of this invention can be used to produce articles that requirecorrosion resistance, toughness and exceptional wearing properties. theform of deep drawing dies,

wear guides; forming rolls, etc.

The articles may take The alloy can. also be extruded into weldrods orweld Y 4 thecopper aluminum iron alloy to be used as die materialsgreatly improves the resistance to surface oxidation, improves thetoughness andwear resistance of the alloy and makes it less susceptibleto eutectoid embrittlement.

Various modes of carrying .out the invention are contemplated as beingwithin the scope of the following claims particularly pointing out and{distinctly claiming the subject matter which is regardedas theinvention.

1. An aluminum-bronze alloy consistingessentiallyof 13.0% to 20.0%aluminum,from 1.0% 'to'8.0% 'i'r'ori, from 0.5% to 3.0% chromiuma'ndtherbalance beihgsubstantially copper, said alloy beingcharacterized by having excellent corrosion resistance and havingimproved toughness and wear resistance.

2. An aluminum bronze alloy consisting essentially of 13.0% to 20.0%aluminum, from;-1.0% .to 8.0% iron, from 0.5 to 3.0% chromium and thebalance being substantially copper, sai-d alloy having a hardness in therange of 25 to Rockwell C and being characterized by having improvedcorrosion resistance, toughness and wear resistance. v

3. An aluminum bronze alloy having improvedcorrosionresistance,'toughness and wear resistance, consisting essentially of13.01% aluminum, 4.13% iron, 1.51% chromium and the balance copper.

4. An aluminum bronze alloy welding electrode, .consisting essentiallyofl3.0%' to -20.0% aluminum, from 1.0% to 8.0% iron, from 0.5 to 3%chromium and the balance being substantially copper.

' 5. A. die for use in working a metal selected from the groupconsisting of stainless steel, aluminum, nickel, titanium, mild steeland copper base alloys, said die being fabricated from au aluminumbronze alloycon sisting essentially of 13.0% to'20.0% aluminum, from1.0% to 8.0% iron, from 0.5% to 3.0% chromium and the balance beingsubstantially copper, said alloy having a hardness in the range of 25 to55 Rockwell C and being characterized by having improved corrosionresistance, toughness and wear resistance.

References Cited in thefile of this patent UNITED STATES PATENTS 537,404f Great Britain j. Sept. 18, 1940

1. AN ALUMINUIM BRONZE ALLOY CONSISTING ESSENTIALLY OF 13.0% TO 20.0%ALUMINUIM, FROM 1.0% TO 8.0% IRON, FROM 0.5% TO 3.0% CHROMUIM AND THEBALANCE BEING SUBSTANTAILLY COPPER, SAID ALLOY BEING CHARACTERIZED BYHAVING EXCELLENT CORROSION RESISTANCE AND HAVING IMPROVED TOUGHNESS ANDWEAR RESISTANCE.